This invention relates generally to catheter-type apparatus for use in treating a subject, and, more particularly, to a device and a related method for positioning a wire along a guide catheter.
Numerous forms of brachytherapy, such as intravascular radiotherapy, involve inserting a guide catheter within a subject, followed by inserting a wire within a lumen in the guide catheter. In some medical uses, the position of a longitudinal portion of the wire, with respect to the portion of the subject's body that requires treatment, can be is critical. Furthermore, accurate control through a plurality of such positions can likewise be critical.
For example, typical intravascular radiotherapy is performed by advancing a flexible guide catheter through a subject's cardiovascular system until the catheter's distal tip is located immediately past the vessel region to be treated, e.g., the region previously subjected to an angioplasty procedure. The guide catheter can be precisely located with respect to the vessel region using known external scanning techniques. An afterloader then advances a wire, having a radiation source at or near its tip (i.e., a radiation source wire), along a lumen of the guide catheter until the radiation source is positioned proximate to the vessel region to be treated.
The radiation source is held in this region for a prescribed time period that is calculated to deliver an effective dosage of radiation to the region. If the region to be treated is longer than the radiation source can effectively treat from one position, the radiation source is longitudinally moved to a second position, generally immediately adjacent to the previous position, to irradiate a second region of the vessel. After another interval, additional movements may be made to irradiate other areas to be treated. When the areas have all been irradiated, the source wire is withdrawn back into the afterloader.
Precisely positioning the wire's radiation source within the guide catheter, however, is problematic. The precise insertion position of the radiation source depends on the length of wire extending into the lumen, the circumference and length of the lumen, and the amount of bunching up that occurs due to the clearance between the wire and the guide catheter. While the guide catheter can be manufactured with precise tolerances, the amount of bunching (i.e., excessive curvature) on any given insertion depends on many factors, and is not easily determined. Furthermore, the amount of bunching can change during the movement of the wire between positions, further adding to the difficulty.
One method previously used to compensate for this problem is to overshoot the desired position with the radiation source, and then withdraw the wire to back the radiation source into the one or more positions. First, the wire is inserted into the guide catheter far enough to cause the radiation source to definitely overshoot its target position. Next, the wire is pulled back to straighten out (unbunch) the wire to remove the excess curvature and pull the radiation source to its first desired position. The wire is again pulled by prescribed amounts to reach other desired positions. This method, however, requires a guide catheter with a lumen that extends past the target position(s), providing room for the wire to overshoot the target position(s). This precludes having a target position at or near the end of the guide catheter. This limitation becomes critical when using the guide catheter in particularly small or delicate locations, such as coronary arteries, where little room exists for a guide catheter to extend beyond the treatment region.
This problem is typical in forms of brachytherapy involving the precise insertion of a wire within a guide catheter's lumen. Accordingly, there has existed a definite need for a device and a related method for positioning a longitudinal portion of a wire within a guide catheter. The present invention satisfies these and other needs, and provides further related advantages.